Viscometric Study of Poly(2-cinnamoyloxyethyl methacrylate)

Well-shaped poly(dimethylsiloxane)-based copolymer nanowires from spherical micelles via kinetic shape evolution

The formation of self-assembled arrays or superstructures from copolymers has attracted intense research interest. Herein, we propose a kinetic approach to form self-assembled nanowires using a PDMS-based block copolymer consisting of poly(dimethylsiloxane)-b-poly[2-(cinnamoyloxy)ethyl methacrylate] (PDMS-b-PCEMA). The copolymer was synthesized by using the macroinitiator PDMS-Br to initiate 2-(trimethylsiloxy)ethyl methacrylate (HEMA-TMS) via ATRP, followed by hydrolysis of the TMS group and gradual esterification with cinnamoyl chloride. PDMS-b-PCEMA presented core-shell spherical micelles in tetrahydrofuran, which transformed into nanowires within 5 days self-assembly via a typical kinetic shape evolution. The diameter of the assembled nanowires with a PCEMA inner core and PDMS shell was about 25-35 nm. The formation of these nanowires reflected a balance between the PDMS and PCEMA components: the PDMS segment was soluble enough to form a corona block, which was beneficial for the transformation of the micellar shape. Meanwhile, the PCEMA segment was able to control the diameter of the nanowire micelles but had no decisive effect on their formation. The effect of solvents on the self-assembled micelles indicated that nanowires were formed in tetrahydrofuran and dichloromethane, while core-shell micelles were formed in acetone. This was due to the different permittivities of these solvents. The nanowires were fixed by cross-linking the PCEMA group under UV irradiation, which enhanced their stability. We believe that this work provides a new strategy for the formation of nanowires and offers a guide for the diversified self-assembly of nanostructures from copolymers.

Versatile Preparation of Branched Polylactides by Low-Temperature, Organocatalytic Ring-Opening Polymerization in N-Methylpyrrolidone and Their Surface Degradation Behavior

We describe how the organocatalytic, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)-based lactide ring-opening polymerization can be effectively performed in a very polar solvent, N-methylpyrrolidone (NMP). Due to a low ceiling temperature, this "living" mechanism has been unreported to date, but we here demonstrate that through a combination of low temperature and repeated monomer additions (starve-fed process), this mechanism enables the generation of a plethora of multifunctional homo- and (stereo)block-poly(lactide)s (PLAs) with exquisite control of the molecular weight dispersity (typically Đ < 1.1) and topology (from linear through 4-, 6-, or 8-armed stars and up to ∼140 armed combs). They are scarcely obtainable or inaccessible through more classical synthetic methods due to the poor solubility of multifunctional initiators (polyols) in most organic solvents and monomer melts. In these precisely designed structures, branching significantly altered the nature of the materials' hydrolytic degradation, allowing them to acquire a pronounced surface character (as opposed to the bulk degradation of linear polymers). Finally, we have assessed the amenability of this method to in situ block copolymerization by using the tacticity of PLLA blocks in PLLA-b-PDLLA versus PDLLA-b-PLLA (L-LA polymerized before or after DL-LA) as a sensitive method to detect (stereochemical) defects.

Optically healable polyurethanes with tunable mechanical properties

The mechanical properties of polyurethanes can be nicely tuned by UV irradiation in a reversible way, endowing the polyurethanes with optical healing properties.

Caracterização viscosimétrica de nanocompósitos híbridos PS/POSS

Nanocompósitos híbridos de poliestireno (PS) e poliedros oligoméricos silsesquioxanos (POSS) com diferentes composições e graus de hibridização foram obtidos por processamento reativo no estado fundido utilizando-se peróxido de dicumila (DCP) como iniciador, na presença ou não de estireno como agente de transferência de radical. Os materiais foram caracterizados viscosimetricamente por cromatografia de permeação em gel (GPC) usando detecção tripla por espalhamento de luz, viscosimetria e índice de refração. As amostras PS/POSS processadas com estireno apresentaram maiores valores de massa molar ponderal média (Mw) e menores valores de polidispersão (Mw/Mn), devido ao maior grau de conversão da reação de hibridização do PS-POSS (28-40%) e do menor grau de degradação (cisão) das cadeias do PS, quando comparadas com amostras PS/POSS processadas sem estireno nas quais o grau de conversão ficou em torno de 24-28%. Para os sistemas PS e PS/POSS em solução com THF, os parâmetros da equação de Mark-Houwink-Sakurada (MHS), α ≅ 0,7 e log K ≅ -3,5 a -3,9 e os valores dos parâmetros de interação polímero-solvente, χij ≅ 0,49, não apresentaram diferenças significativas com relação aos tamanhos moleculares. Por outro lado, essas diferenças de tamanhos moleculares foram caracterizadas por uma função cumulativa da fração mássica de cadeias em função da distância média quadrática entre pontas de cadeia (< r² >0½).