MALDI-TOF Mass Spectrometric Characterization of Polyacrylamide Multiblock Copolymers Reveals Structure–Property Relationships

Abstract A novel series of multiblock copolymers composed of alternating poly(N-acryloylmorpholine) (PNAM) and poly(N-isopropylacrylamide) (PNIPAM) segments were synthesized using reversible addition–fragmentation chain-transfer (RAFT) polymerization to explore the relationship between molecular architecture and thermoresponsive behavior. The synthesis was conducted stepwise, enabling precise control over block length and composition. Comprehensive characterization was performed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) with our previously reported data processing methodology, supported by 1H NMR and size-exclusion chromatography (SEC). This detailed structural analysis enabled rigorous evaluation of the sequential RAFT synthesis and provided the molecular-level information required to establish quantitative structure–property relationships in the multiblock copolymers. The designed and experimentally determined degrees of polymerization showed excellent correlation (r = 0.983), confirming high synthetic precision. Turbidimetry measurements revealed tunable lower critical solution temperature (LCST)-type phase transitions, where alternating PNIPAM and PNAM blocks produced systematic, reversible shifts in aggregation temperature. This iterative approach enables the predictive design of block copolymers with tailored thermoresponsive properties, offering significant potential for applications in drug delivery, tissue engineering, and smart materials.