Julie L P Jessop

University of Iowa, Iowa City, Iowa, United States

Are you Julie L P Jessop?

Claim your profile

Publications (14)28.76 Total impact

  • Brian Dillman, Julie L. P. Jessop
    [Show abstract] [Hide abstract]
    ABSTRACT: The effects of chain transfer agents (CTA) on cationic ring-opening polymerization of 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexane carboxylate (EEC) were explored. EEC was polymerized in the presence of various CTAs, and epoxide conversions monitored via Raman spectroscopy. Polymer films were prepared and analyzed by dynamic mechanical analysis. Many of the organic alcohols studied greatly enhanced epoxide polymerization rates and conversion levels. The gel fraction of polymer specimens decreased rapidly with increasing amounts of octanol (gel fraction >90% up to 0.3 equiv OH) but remained high with increasing amounts of 1,2-propanediol (gel fraction >90% up to 0.6 equiv OH). Increasing the size of primary alcohols had little effect on the polymerization rates and conversions. The polymerization rate decreased with increasing alcohol substitution (1°>2°>3°). Acidic alcohols had very low impact on conversion and polymerization rates relative to the neat epoxy resin. The glass transition temperature was inversely related to the size and amount of CTA. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013
    Journal of Polymer Science Part A Polymer Chemistry 05/2013; 51(9):2058-2067. · 3.54 Impact Factor
  • Brian F. Dillman, Na Yeon Kang, Julie L.P. Jessop
    [Show abstract] [Hide abstract]
    ABSTRACT: A simple, low environmental impact procedure for preparing acrylated castor oil (ACO) was developed using a hybrid acrylate isocyanate monomer. The photopolymerization of neat ACO and the co-polymerization of ACO with common low molecular weight acrylate monomers were rapid and reached high conversions, as monitored by real-time FT-IR spectroscopy. The mechanical properties of the ACO polymers and copolymers were determined by dynamic mechanical analysis of the thin polymer films. The resulting copolymers ranged from highly flexible, low glass transition materials to rigid, high glass transition materials depending on the functionality and secondary functional groups of the commercial monomers used. The ACO oligomer was compatible with a variety of acrylate monomers and produced transparent films regardless of co-monomer used. The glass transition temperatures of the copolymers can be coarsely estimated a priori using the Fox correlation. ACO-based materials provide a promising route to introduce renewable materials in many acrylate-based coating applications.
    Polymer. 03/2013; 54(7):1768–1774.
  • Source
    Yuan Zou, Julie L P Jessop, Steven R Armstrong
    [Show abstract] [Hide abstract]
    ABSTRACT: Penetration of adhesives into the demineralized dentin surface and their subsequent conversion are critically important to longevity of the adhesive resin (AR)-dentin bond. The durability of the resin-dentin bond is investigated by monitoring the change of adhesive concentration within the hybrid layer (HL) of aged specimens using Raman spectroscopy. Absolute molar concentrations of Bis-GMA and HEMA were measured across the HL of resin-dentin specimens 24 h after photopolymerization and after 24-week storage in one of three media: artificial saliva (SAL), SAL containing cholesterol esterase to attack resin (EST), and SAL containing bacterial collagenase to attack collagen (COL). No significant difference among these groups for both Bis-GMA and HEMA molar concentrations at 24-h storage was found; however, concentrations decreased from the AR to the middle of the HL. Concentrations remained unchanged at any resin-dentin position after aging in SAL. In the HL, concentrations significantly decreased with aging in COL and tended to decrease in EST. While showing potential enzymatic biodegradative effects of endogenous matrix metalloproteinases and salivary esterases, this methodology may also prove to be a valuable assessment of new chemistries and future approaches to improve resin-dentin bond performance. (c) 2010 Wiley Periodicals, Inc. J Biomed Mater Res, 2010.
    Journal of Biomedical Materials Research Part A 07/2010; 94(1):187-92. · 2.83 Impact Factor
  • Source
    Yuan Zou, Steven R Armstrong, Julie L P Jessop
    [Show abstract] [Hide abstract]
    ABSTRACT: The objective was to determine absolute molar concentration of adhesive resin components in the hybrid layer by establishing methods based on Raman spectroscopy fundamentals. The hybrid layer was treated as a three-component system consisting of collagen and an adhesive resin containing two monomers. Adhesive standard specimens and Raman peak area ratios obtained with a 785 nm excitation wavelength were used to construct separate calibration curves for comonomer relative molar concentration and Bis-GMA absolute molar concentration. As collagen and water had no measurable peaks in the fingerprint region, a dilution coefficient K(j) was defined to describe their impact on Raman peak area and to calculate HEMA absolute molar concentration. Methodology was validated using an analogous system containing acetone/ethanol/water. The absolute molar concentration of Bis-GMA and HEMA decreased 87% and 83%, respectively, from the top quarter to the middle of the hybrid layer. Additionally, less Bis-GMA penetrated the hybrid layer than HEMA, as indicated by the approximately 20% decrease in comonomer molar concentration ratio between the adhesive resin layer and the top half of the hybrid layer. Lack of complete monomer infiltration will further challenge dentin-adhesive bond longevity. (c) 2010 Wiley Periodicals, Inc. J Biomed Mater Res, 2010.
    Journal of Biomedical Materials Research Part A 02/2010; 94(1):288-97. · 2.83 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: To examine the degree of conversion (DC) of the adhesive interfaces created by Filtek Silorane Adhesive and Clearfil SE Bond using micro-Raman spectroscopy. The adhesives were applied on human dentin in accordance with manufacturer's instructions. Specimens were cut to expose the bonded interfaces to the micro-Raman beam (Ranishaw InVia; laser wl 785 nm). Raman spectra were collected along the dentin/self-etching primer/adhesive interface at 1 microm intervals. The relative intensities of bands associated with mineral (P-O functional group at 960 cm(-1)) and adhesive (C-C-O group at 605 cm(-1)) components within the bonded interface were used to detect monomer penetration into the dentin matrix and to calculate the degree of conversion (C=C at 1640 cm(-1) as reaction peak, C-C-O at 605 cm(-1) as reference peak). Data were statistically analyzed with two-way ANOVA. DC of Filtek Silorane Adhesive was 69+/-7% in the adhesive layer, increasing (p<0.05) to 93+/-5% in the primer and 92+/-9% in the hybrid layer. Clearfil SE Bond showed a DC of 83+/-3% in the hybrid and 85+/-3% in the adhesive layer. Thus, Filtek Silorane Adhesive showed a higher DC than Clearfil SE Bond in the hybrid layer (p<0.05), but a lower DC in the adhesive (p<0.05). As high DC is a fundamental pre-requisite for the stability of the bond over time, this study supports the hypothesis that optimal stability of Filtek Silorane Adhesive can be obtained. However, further research is needed to investigate the mechanical properties of the hybrid layer created by Filtek Silorane Adhesive and its long-term stability.
    Dental materials: official publication of the Academy of Dental Materials 07/2009; 25(9):1178-85. · 2.88 Impact Factor
  • Ying Cai, Julie L.P. Jessop
    [Show abstract] [Hide abstract]
    ABSTRACT: Photopolymerization systems based on hybrid monomer 3,4-epoxy-cyclohexylmethyl methacrylate (METHB) were studied to investigate water effects on conversion and polymer coating properties. METHB contains epoxide and methacrylate moieties, which undergo cationic and free-radical photopolymerization, respectively. The conversion of both groups was obtained by Raman spectroscopy in real time and depth. Water concentration and initiator system compositions were varied and shown to affect reaction kinetics and depth profile. With increasing water concentration, the epoxide induction period increased when only cationic initiator was present; however, the induction period disappeared when using the dual-initiator system. In addition, epoxide groups continued reacting after light was shuttered and reached a higher and more homogeneous conversion. Hybrid systems were shown to be less sensitive to water at low or intermediate concentrations. With high water concentrations, hybrid monomer systems manifested increased ring opening during illumination due to chain transfer and decreased physical properties due to loss of cross-linking.Graphical abstract
    Polymer. 01/2009; 50(23):5406-5413.
  • Chris M. Comer, Julie L. P. Jessop
    [Show abstract] [Hide abstract]
    ABSTRACT: Starch-g-poly(methyl methacrylate) (PMMA) was prepared by emulsion photopolymerization without photoinitiator. Grafting efficiency was determined for two types of starch (high-amylose and amylopectin) and at several illumination times. Since clogging of the graft copolymer prevented vacuum filtration and Soxhlet extraction was too time-consuming, a new method to separate the PMMA homopolymer from the graft copolymer was developed. Back-flush filtration uses an intermittent pressure pulse to clean the filter as the homopolymer is separated from the graft copolymer. Back-flush filtration was shown to be more efficient by reducing the separation time and solvent use, and the grafting efficiencies obtained with back-flush filtration compare favorably with those from Soxhlet extraction for the starch-g-PMMA copolymer systems studied. More accurate grafting efficiencies could be obtained by applying a nonstick coating to the inside chamber of the back-flush filtration unit.
    Starch - Starke 07/2008; 60(7):335 - 339. · 1.22 Impact Factor
  • Yuan Zou, Julie L P Jessop, Steven R Armstrong
    [Show abstract] [Hide abstract]
    ABSTRACT: Penetration and conversion of adhesives into the hybrid layer (HL) is important to the quality and longevity of the adhesive resin (AR)-dentin bond. In this study, a methodology is developed to examine the degree of conversion and relative HEMA concentration with respect to Bis-GMA using Raman spectroscopy. This methodology will be used in the future reports related to this topic. Conversion in the AR of water-stored resin-dentin samples (84% +/- 3%) agreed well with that measured in commercial adhesive (Comm Adh) resin samples after 24-h water storage (80% +/- 2% from Part 1) and was significantly higher than Comm Adh without water storage (58% +/- 3% from Part 1) (p = 0.0005). Adhesive conversion was not significantly different (p = 0.5036) through the middle of the HL, with a mean of 83% +/- 6%. HEMA mole fraction, relative to Bis-GMA, was significantly higher (p = 0.0028) in the top half of the HL (0.67 +/- 0.03), when compared to HEMA in the AR (0.60 +/- 0.01). HEMA and EDMAB were identified through GC/MS as leachable components in the aqueous 24-h storage media. The effect of this elution explains the change in conversion measurements observed between dry and water-stored conditions, which is more appropriately described as the "apparent" conversion.
    Journal of Biomedical Materials Research Part A 05/2008; 89(2):355-62. · 2.83 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: To measure the denaturation temperature (Td) of demineralised dentine matrix as a function of infiltration with water vs. polar solvents vs. adhesive resins. Small discs of normal dentine were completely demineralised in 0.5M EDTA. Dried demineralised specimens were placed in water, methanol, ethanol, acetone, eta-butanol or HEMA. Additional specimens were infiltrated with Prime&Bond NT and polymerised. All specimens sealed in high-pressure pans and scanned using differential scanning calorimetry (DSC). Demineralised dentine saturated with water showed a Td of 65.6 degrees C that increased with saturation by methanol, ethanol, acetone, eta-butanol or HEMA to 148.5 degrees C. These increases in Td were inversely related to the molar concentration of the solvents and to their Hoy's solubility parameter for hydrogen bonding (delta h, p<0.01), as well as directly related to the cube root of their molecular weights (p<0.001). The presence of adhesive resins also increased the Td of demineralised matrices to even higher values depending if the resin bonded dentine was measured after 24h of water storage (166.8 degrees C) or dry (172.7 degrees C) storage. Solvents and monomers with low delta(h) values (i.e., 100% HEMA) increase the Td of demineralised dentine above that produced by solvents with higher delta h values such as methanol and water.
    Journal of Dentistry 01/2008; 36(1):8-14. · 3.20 Impact Factor
  • Yuan Zou, Steven R Armstrong, Julie L P Jessop
    [Show abstract] [Hide abstract]
    ABSTRACT: Monomer conversion of adhesives in the hybrid layer is important to the quality and longevity of the dentin bond. In this study, degree of conversion and relative co-monomer concentrations of both experimental and commercial adhesive resins were determined using Raman spectroscopy. The objectives were to identify stable Raman scattering peaks to use as internal references and to determine the effect of water storage on measured conversion and co-monomer concentrations. The peak at 605 cm(-1) did not change throughout polymerization and is associated with monomers in both adhesives. This peak was used as an internal reference for conversion and composition calculations before and after water storage. Conversion of the adhesive resins immediately after photopolymerization was approximately 20% lower than that measured after 24-h water storage. HEMA concentration (relative to bis-GMA) in the adhesive resins immediately after photopolymerization was at least 5 wt % higher than that measured after 24-h water storage. Elution of unreacted HEMA provides a reasonable explanation for the "supposed" change in conversion measurements, which is more appropriately described as apparent conversion. This apparent conversion will impact interpretation of physical properties and structure of the polymer, as well as increase the probability of water penetration and its reaction within the hybrid layer.
    Journal of Biomedical Materials Research Part A 12/2007; 86(4):883-91. · 2.83 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The denaturation temperature (T(d)) of dentin collagen in mineralized versus demineralized teeth was examined as a function of dentin age and the extent of dehydration. Using differential scanning calorimetry, T(d) of mineralized dentin was shown to be between 160 degrees C to 186 degrees C, depending on whether it was from young or old dentin that was hydrated or dehydrated, respectively. Demineralized dentin exhibited a T(d) of 65.6 degrees C that increased with dehydration to 176 degrees C. The presence of apatite crystallites or interpeptide bonding increased the T(d) of demineralized matrices. Interpeptide hydrogen bonding seems to stabilize collagen to thermal challenge. Water breaks interpeptide hydrogen bonds making collagen more susceptible to thermal denaturation. Rises in intracanal temperature are unlikely to cause extensive denaturation of mineralized root dentin walls. However, hydrated or partially dehydrated root canal walls that have been partially demineralized with chelating agents or mild acids may be susceptible to thermal denaturation.
    Journal of Endodontics 08/2006; 32(7):638-41. · 2.93 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The purpose of this work was to determine microtensile dentin bond strengths (microTBS) of dentin-resin composite bonds after three-month storage in artificial saliva containing either collagenase (COL) or cholesterol esterase (EST). The null hypothesis tested is that the resin-dentin bond strength is equivalent for each storage medium at the tested storage times. Resin composite was bonded to occlusal dentin, and microTBS specimens were formed and stored in the artificial saliva, COL, EST, or synthetic oil. After 24 h and 12-week storage, microTBS was determined and failure modes were characterized by SEM. The interfacial ultrastructure was evaluated by transmission electron microscopy as unstained and stained sections (phosphotungstic acid/uranyl acetate). Statistical analysis was performed by ANOVA and Weibull survival analyses at the 0.05 level of statistical significance. There were significantly weaker bond strengths after 12 weeks for all experimental storage media (p < 0.001). Artificial saliva containing EST lowered bond strengths to a significantly greater extent than did COL after 12 weeks of storage, while no difference between these groups could be discerned after 24 h. Therefore, the null hypothesis of this experiment is rejected. Exogenous enzymatic challenge to resin-dentin bonds decreased bond durability only with EST. However, when further challenges to ideal infiltration of the comonomers into the hybrid layer were carried out using inadequate removal of solvent, additional alterations in hybrid layer ultrastructure were discerned by TEM that may represent different potential degradative processes. The contribution of endogenous enzymatic challenges to the primary degradative process, ie, hydrolysis, is unknown and deserves continued attention.
    The journal of adhesive dentistry 06/2006; 8(3):151-60. · 0.91 Impact Factor
  • Ying Cai, Julie L.P. Jessop
    [Show abstract] [Hide abstract]
    ABSTRACT: Photopolymerization systems based on hybrid monomer 3,4-epoxy-cyclohexylmethyl methacrylate (METHB) were studied to investigate the oxygen inhibition effects on the conversion and polymer properties in films and coatings. METHB contains epoxide and methacrylate functional groups, which undergo cationic and free-radical photopolymerization, respectively. The conversion of both groups was obtained by Raman confocal microscopy as a function of depth. Initiator system compositions were varied and shown to affect the depth profile. The methacrylate group conversion was low at the surface due to oxygen inhibition. When both reactions were present, a cross-linked network formed and reduced oxygen sensitivity. At depths greater than the oxygen-diffusion-affected region, both functional groups' conversions did not show depth dependence. In addition, epoxide groups continued reacting after light was shuttered and reached a higher and more homogeneous conversion. These systems exhibit lower sensitivity to oxygen and offer advantages such as increased cure speed and improved film-forming properties compared to free-radical systems.
    Polymer. 01/2006;
  • [Show abstract] [Hide abstract]
    ABSTRACT: The use of thick sections of fiber-reinforced polymers (FRPs) is increasing for numerous industrial applications such as wind turbine blades. In situ cure monitoring is very important to directly observe the cure process of FRPs during the manufacturing process. In this work, Raman spectroscopy and dielectric analysis (DEA) are investigated for in situ cure monitoring of an epoxy resin. The cure behavior is first characterized using differential scanning calorimetry (DSC) as a baseline comparison, and the best-fit phenomenological reaction model is determined to describe the cure behavior of the epoxy resin as well as the kinetic parameters. The relationship between Tg and degree of cure is also established. The degree of cure obtained from Raman spectroscopy and DEA under isothermal conditions is compared to that obtained from DSC. A good agreement is observed among the three methods, supporting the potential of these in situ cure monitoring methods during manufacturing. An implementation plan for in-plant monitoring is also discussed.
    Composites Part A Applied Science and Manufacturing 49:100–108. · 2.74 Impact Factor