Bisphenol-A polycarbonate produced by interfacial phosgenation of 2,2-bis(4-hydroxyphenyl)propane and by melt transesterification with diphenyl carbonate enters global supply chains under two principal trade names. The technical comparison summarized as “Makrolon vs Lexan: Two Polycarbonate Trade Names, Two Continents, One Polymer” is, at the polymer-backbone level, a comparison of identical bisphenol-A polycarbonate with different manufacturing genealogies, additive packages, and certificate portfolios. Makrolon is associated with European production and Covestro’s Leverkusen lineage; Lexan is associated with the GE Plastics heritage in North America and now with SABIC’s global portfolio. The repeat unit is identical: 2,2-bis(4-hydroxyphenyl)propane polymerized through carbonate linkages, producing an amorphous polymer with a glass transition temperature of approximately 147 °C by differential scanning calorimetry to ISO 11357-2 and no crystalline melting point. Commercial unfilled grades typically exhibit density of 1.19–1.20 g/cm³ under ISO 1183-1:2019 and visible-light transmission of 88–90% in a 3.0 mm plaque under ISO 13468-1. The carbonate linkage, not the trade name, governs the polymer’s hydrolytic sensitivity, UV stability, and notch response.

Molecular Architecture Does Not Change With the Hemisphere of Manufacture

Commercial Makrolon and Lexan grades are both produced from bisphenol A and a carbonate source; the interfacial route uses phosgene in an aqueous-organic two-phase system with a tertiary amine catalyst, while the melt route uses diphenyl carbonate with transesterification catalysts. The resulting polymer contains the same carbonate-linked aromatic repeat unit, with weight-average molar mass typically in the range of 18,000–36,000 g/mol for injection and extrusion grades. Polydispersity measured by gel permeation chromatography generally lies between 2.0 and 3.0. These molecular weight differences, not continental origin, control melt volume-flow rate under ISO 1133-1:2022 and capillary viscosity under ISO 11443. Higher molar mass extrusion grades reduce MVR to 3–6 cm³/10 min at 300 °C and 1.2 kg, while high-flow optical grades may reach 15–25 cm³/10 min. The polymer remains amorphous; stress relaxation, mold shrinkage, and birefringence arise from frozen-in orientation rather than crystallinity. End-group concentration, residual monomer, and ionic residues differ between interfacial and melt polymerization and can shift hydrolytic stability even when the backbone is identical.

Why Do Processors Observe Viscosity Differences Between Two Nominally Identical Grades?

Datasheet equivalence based solely on MVR often fails because ISO 1133-1:2022 reports a single shear-stress condition and does not capture the full viscosity curve. Capillary rheometry under ISO 11443 at shear rates from 100 s⁻¹ to 10,000 s⁻¹ shows that a 10 g/10 min Makrolon grade and a 10 g/10 min Lexan grade may diverge by more than 5–10% in apparent viscosity at 1,000 s⁻¹ when additive packages, release-agent loadings, and stabilizer types differ. Typical additive systems include phosphite or hindered phenol heat stabilizers, pentaerythritol tetrastearate mold release at 0.2–0.5 wt%, benzotriazole UV absorbers, and blue toners. These additives influence low-shear viscosity, mold deposit rates, and optical color but do not alter the bisphenol-A carbonate backbone. Processors must therefore treat trade-name substitution as a re-qualification exercise: tensile properties under ISO 527-2/1A/50, notched impact under ISO 180/A, and flammability certification under UL 94 are grade-specific, not merely polymer-specific. Published data for direct substitution of one brand for another in long-term creep or fatigue is limited; design engineers should request grade-specific creep modulus and fatigue data rather than assuming interchangeability.

Values represent published databook ranges for unfilled medium-viscosity injection grades; current grade-specific datasheets must be used for specification and mold design.

Rheologically, the two trade-name families diverge most visibly in thin-wall molding. Thin-wall electronic housings with wall thickness below 1.0 mm require melt temperatures above 300 °C and injection velocities above 150 mm/s to prevent premature freeze-off. Cavity pressure sensors are used to switch from velocity to pressure control at typical switch-over pressures of 60–80 MPa. Pressure drop through hot-runner systems and gate geometries should be calculated using grade-specific viscosity coefficients, not generic polycarbonate data. Grade-specific coefficients for Cross-WLF or Carreau models are normally available from both trade-name suppliers, but the coefficients differ with molar mass, filler content, and flame-retardant additives.

At the molding machine, residual moisture rather than trade-name selection is the dominant source of process variation. Desiccant hopper dryers must deliver air at a dew point of ≤ -40 °C and a hopper temperature of 120 °C. Virgin pellets from sealed containers generally require 4 h drying; pellets stored at relative humidity above 60% or regrind may require 6–8 h. Maximum residual moisture should be 0.02 wt% for optical parts and 0.05 wt% for non-optical parts, measured by ASTM D6869 or ISO 15512 method C. Barrel profiles from feed to nozzle are typically set from 260 °C to 300–320 °C, with melt temperature verified by insertion pyrometer. Residence time should remain below 6 min at temperature; longer residence leads to molecular weight loss and yellowing. Mold temperatures of 80–120 °C control surface gloss, mold shrinkage, and residual stress. Form errors and birefringence in transparent molded parts are minimized with mold temperatures in the 110–120 °C range and lower injection velocities, but cycle time increases. The processing window is not a trade-name property; it shifts with molar mass, additive package, and part thickness.

When Flame-Retardant Grades Are Exposed to Glow-Wire Testing and Outdoor Weathering

Specifications such as UL 94 V-0 at 0.75 mm or 1.5 mm, UL 94 5VA at 3.0 mm, and glow-wire flammability index of 960 °C at 2.0 mm under IEC 60695-2-12 are common for electrical enclosures. Flame-retardant Makrolon and Lexan grades achieve these ratings through additive systems, often phosphate ester-based, that modify the char-forming and dripping behavior of polycarbonate. The same additives can reduce heat deflection temperature under ISO 75-2/Af by up to 5–15 °C relative to unfilled grades and may increase plate-out on mold surfaces. For outdoor UV exposure, UL 746C f1 outdoor suitability and accelerated weathering under ISO 4892-2 should be specified grade by grade; published data for a general-purpose transparent grade does not automatically transfer to a flame-retardant or glass-reinforced grade. Dielectric strength under IEC 60243-1 and comparative tracking index under IEC 60112 should also be re-verified after additive changes.

In food-contact and medical device applications, the regulatory status of the final article depends on grade-specific additives and monomer migration rather than the polymer family alone. Unfilled polycarbonate may be formulated to comply with FDA 21 CFR 177.1580 and EU 10/2011, but each grade must be verified for overall migration limits, including the 10 mg/dm² overall migration default under EU 10/2011 for many food simulants. Steam autoclaving at 121 °C can induce haze after repeated cycles, and gamma sterilization at 25–50 kGy can produce yellowing from free-radical damage; ethylene oxide sterilization is less aggressive but requires residue testing per ISO 10993-7. Biocompatibility under ISO 10993-1 is a final-device assessment and cannot be inferred solely from a Makrolon or Lexan medical grade designation. Aqueous contact above 60 °C accelerates hydrolysis at the carbonate linkage, reducing molar mass and tensile properties. Published data comparing the long-term hydrolytic aging of the two trade-name families in controlled water contact are limited, so accelerated aging under ISO 22088-2 or similar should be performed for the actual service environment.

Listing does not imply that all Makrolon or Lexan grades meet all listed standards.

During sheet and multiwall extrusion, transparent PC from either trade-name family typically runs on single-screw or vented twin-screw extruders with L/D ratios of 30:1–36:1 and polished steel polishing roll stacks. Melt temperatures are held near 280–300 °C, while polishing roll temperatures are operated in the 100–140 °C range to control surface replication and internal stress. Moisture control remains the dominant variable: residual moisture above 0.02 wt% produces bubble-like specks, silver streaks, and localized thickness variation. Extrusion grades have higher molar mass and may require higher torque and back pressure; melt fracture at the die lip is controlled by die-gap adjustment and melt filtration rather than brand substitution. Coextruded UV-capped sheet uses a thin cap layer containing concentrated UV absorbers; the cap layer’s adhesion and weathering performance must be re-qualified for each grade combination.

Transport interior and lighting applications require heat deflection under ISO 75-2/Af, notched impact at sub-zero temperature under ISO 180/A at -30 °C, and resistance to long-term heat aging at 125 °C. Both trade-name families supply grades for these applications, but molding trials on the actual tool are required because flow length, thickness, and additive package shift the effective processing window beyond what datasheet MVR indicates.