Digital Light Processing to Afford High Resolution and Degradable CO2-Derived Copolymer Elastomers.

Vat photopolymerization 3D printing has proven very successful for the rapid additive manufacturing (AM) of polymeric parts at high resolution. However, the range of materials that can be printed and their resulting properties remains narrow. Herein, we report the successful AM of a series of poly(carbonate-b-ester-b-carbonate) elastomers, derived from carbon dioxide and bio-derived ϵ-decalactone. By employing a highly active and selective Co(II)Mg(II) polymerization catalyst, an ABA triblock copolymer (Mn=6.3 kg mol-1, ÐM=1.26) was synthesized, formulated into resins which were 3D printed using digital light processing (DLP) and a thiol-ene-based crosslinking system. A series of elastomeric and degradable thermosets were produced, with varying thiol cross-linker length and poly(ethylene glycol) content, to produce complex triply periodic geometries at high resolution. Thermomechanical characterization of the materials reveals printing-induced microphase separation and tunable hydrophilicity. These findings highlight how utilizing DLP can produce sustainable materials from low molar mass polyols quickly and at high resolution. The 3D printing of these functional materials may help to expedite the production of sustainable plastics and elastomers with potential to replace conventional petrochemical-based options.

Controlled Carbon Dioxide Terpolymerizations to Deliver Toughened yet Recyclable Thermoplastics.

Using CO2 polycarbonates as engineering thermoplastics has been limited by their mechanical performances, particularly their brittleness. Poly(cyclohexene carbonate) (PCHC) has a high tensile strength (40 MPa) but is very brittle (elongation at break <3%), which limits both its processing and applications. Here, well-defined, high molar mass CO2 terpolymers are prepared from cyclohexene oxide (CHO), cyclopentene oxide (CPO), and CO2 by using a Zn(II)Mg(II) catalyst. In the catalysis, CHO and CPO show reactivity ratios of 1.53 and 0.08 with CO2, respectively; as such, the terpolymers have gradient structures. The poly(cyclohexene carbonate)-grad-poly(cyclopentene carbonate) (PCHC-grad-PCPC) have high molar masses (86 < Mn < 164 kg mol-1, DM < 1.22) and good thermal stability (Td > 250 °C). All the polymers are amorphous with a single, high glass transition temperature (96 < Tg < 108 °C). The polymer entanglement molar masses, determined using dynamic mechanical analyses, range from 4 < Me < 23 kg mol-1 depending on the polymer composition (PCHC:PCPC). These polymers show superior mechanical performance to PCHC; specifically the lead material (PCHC0.28-grad-PCPC0.72) shows 25% greater tensile strength and 160% higher tensile toughness. These new plastics are recycled, using cycles of reprocessing by compression molding (150 °C, 1.2 ton m-2, 60 min), four times without any loss in mechanical properties. They are also efficiently chemically recycled to selectively yield the two epoxide monomers, CHO and CPO, as well as carbon dioxide, with high activity (TOF = 270-1653 h-1, 140 °C, 120 min). The isolated recycled monomers are repolymerized to form thermoplastic showing the same material properties. The findings highlight the benefits of the terpolymer strategy to deliver thermoplastics combining the beneficial low entanglement molar mass, high glass transition temperatures, and tensile strengths; PCHC properties are significantly improved by incorporating small quantities (23 mol %) of cyclopentene carbonate linkages. The general strategy of designing terpolymers to include chain segments of low entanglement molar mass may help to toughen other brittle and renewably sourced plastics.

Toughening CO2 -Derived Copolymer Elastomers Through Ionomer Networking.

Utilizing carbon dioxide (CO2 ) to make polycarbonates through the ring-opening copolymerization (ROCOP) of CO2 and epoxides valorizes and recycles CO2 and reduces pollution in polymer manufacturing. Recent developments in catalysis provide access to polycarbonates with well-defined structures and allow for copolymerization with biomass-derived monomers; however, the resulting material properties are underinvestigated. Here, new types of CO2 -derived thermoplastic elastomers (TPEs) are described together with a generally applicable method to augment tensile mechanical strength and Young's modulus without requiring material re-design. These TPEs combine high glass transition temperature (Tg ) amorphous blocks comprising CO2 -derived poly(carbonates) (A-block), with low Tg poly(ε-decalactone), from castor oil, (B-block) in ABA structures. The poly(carbonate) blocks are selectively functionalized with metal-carboxylates where the metals are Na(I), Mg(II), Ca(II), Zn(II) and Al(III). The colorless polymers, featuring <1 wt% metal, show tunable thermal (Tg ), and mechanical (elongation at break, elasticity, creep-resistance) properties. The best elastomers show >50-fold higher Young's modulus and 21-times greater tensile strength, without compromise to elastic recovery, compared with the starting block polymers. They have wide operating temperatures (-20 to 200 °C), high creep-resistance and yet remain recyclable. In the future, these materials may substitute high-volume petrochemical elastomers and be utilized in high-growth fields like medicine, robotics, and electronics.

Cross-sectional case-control study on medical students' psychosocial stress during COVID-19 pandemic in Hong Kong.

INTRODUCTION: COVID-19 pandemic has resulted in significant changes in pedagogy for undergraduate medical curriculum. Many physical clinical teachings have been replaced by online pedagogy. This study aims to evaluate the relation between medical students' stress during COVID-19 pandemic and their academic performance at the final examination. METHODS: This is a cross-sectional questionnaire-based study. Student's stress level were evaluated by the COVID-19 Student Stress Questionnaire (CSSQ). Correlation of stress level and students' performance at the final examination was performed. RESULTS: 110 out of 221 (49.8%) final-year medical students responded to the questionnaire, 13 students failed in the final examination (case) while 97 students passed in the final MBBS examination (control).Baseline demographic data between case and control were comparable. The median age for both cases and controls were 24 years.Compared to controls, cases reported higher levels of stress in all domains, namely in relation to risk of contagion, social isolation, interpersonal relationships with relatives, university colleagues and professors, academic life, and sexual life. Notably, a significantly higher proportion of cases reported academic-related stress compared to controls (p < 0.01), with 100% of cases perceiving their academic studying experience during the COVID-19 pandemic to be "very" or "extremely" stressful, compared to 35.1% of controls. CONCLUSION: Increased stress to academic and study during COVID-19 was associated with worse examination outcome at the final examination. Extra academic support will be needed to cater students' need during the pandemic.

Pilot assessment of pain of orthopaedic patients in Hong Kong.

This pilot study examined the internal consistency and concurrent validity of the Chinese version of the Acute Lower Back Pain Screening Questionnaire. A sample of 45 acute low back pain patients (27 men and 18 women; mean age = 47.8) were recruited from the Department of Orthopaedics and Traumatology of the Tuen Mun Hospital in Hong Kong. Three items of the original questionnaire were excluded from the analyses because response was low by 30 of the 45 patients. The questionnaire showed good internal reliability (Cronbach alpha = .88) and correlated significantly with other test scores: the Faces Pain Scale-Revised (alpha = .74), the Chinese (Hong Kong) SF-12 Health Survey (Mental subscale, alpha = -.47; Physical subscale alpha = -.62), and the Chinese Hospital Anxiety and Depression Scale (Anxiety subscale, alpha = .42; Depression subscale, alpha = .43). The questionnaire could be used in research and clinical work to provide data on the multicomponents of a pain experience as well as psychosocial risk factors related to pain among the Chinese. Researchers might examine the course of change in chronic pain.